The invention relates a bale press, in particular a square bale press, in which crop material is pressed into a cuboid bale by a piston which is reciprocating in a pressing channel. In order to prevent the bales from disintegrating when ejected from the pressing channel, a yarn is tied around the bales and knotted.
Knotter devices used to wrap bales of crop material are known. For example, EP 2198687 A1 discloses a conventional knotter device that ties yarn around pressed bales of crop material.
Such conventional knotter device comprises a first holder, also referred to as a clamping disk, for releasably holding an end portion of the yarn, a deflecting member or horn around which the yarn is bent, and a knotter beak. The knotter beak ties a knot which connects a first stretch of the yarn extending between the first holder and the deflecting member to a second stretch of yarn which is introduced into the knotter device by a reciprocating needle from across the pressing channel.
When a process of forming/wrapping a particular bale is finished and formation of a new bale is about to begin, the yarn to be wrapped around the new bale extends straight through the pressing channel. When the bale grows, it displaces the yarn in a downstream direction of the channel. Consequently, an intermediate portion is formed which extends in the longitudinal direction of the channel between the first stretch of the yarn extending between the first holder and the deflecting member and a portion of the yarn which extends straight through the pressing channel at a side of the new bale opposite to the piston.
Since one end of the yarn is firmly held by the clamping disk, the length of the intermediate portion can increase only due to yarn which is slips around the bale under formation whenever the bale is pushed down the pressing channel by the strokes of the piston. Since friction at the flanks of the bale increases with the length of the bale, the tension to which the yarn is subjected can become quite high when the bale is nearly finished. Consequently, in many balers of the prior art, the yarn was likely to snap or to slip from the clamping disk at that stage, particularly when the bale is nearly finished.
Various solutions have been proposed for controlling the tension of the yarn, in order to prevent it from snapping or slipping during the bale wrapping process. Typically with these known proposed solutions, even where the tension of the yarn could be safely maintained below its rated tensile strength, snapping could still not be avoided completely, i.e., in every situation.